## 8 Reputation

13 years, 278 days
Munich, Germany

## numerical integral of a complex expressi...

Maple 13

Hi, I would like to numerically work out the profile of one expression (integral and BesselK function involved). But the computer was just jammed and came out nothing after long time waiting. I attach the worksheet below and maybe you could have a look at it or directly run it in your machine to check what is wrong, either my computer or the code itself. Thank you very much.

> restart;
> with(PDEtools); with(Units[Standard]); with(ScientificConstants);

## The solver does not return a result...

> restart;
> ode := `assuming`([(diff(r^2*(diff(`&varphi;`(r), r)), r))/r^2 = k[0]^2*`&varphi;`(r)+Q*Dirac(r)/`ε`[0]], [Q::positive, (`ε`[0])::positive, (k[0])::positive, r::real]);
> ics := `&varphi;`(infinity) = 0, `&varphi;`(-infinity) = 0;
> dsolve({ics, ode}, `&varphi;`(r), method = fourier);
>

I have an ODE...

## How to deal with very small number?...

Maple 13

Hi, everyone, I am sorry that I have to post this question again since the last post sank and I did not give example at that time. In the example I post here, A[e,res1] and A[e,res2] are supposed to be the same theoretically. However, as I  used numeric solver (fsolve), they are 2 order different. Can anyone try the code and tell me what mistakes I made? I appreciate that.

> restart;
> with(PDEtools);
>
>
> # Electron velocity distribution:

## Is it caused by numeric error?...

Maple 13

I want to fsolve one non-linear equation as follows: expr_1/expr_2=C which can not be solvable in maple directly. However, once I use expr_3=simplify(expr_1/expr_2) and then expr_3=C, it returns a result. Something weird happens now. Once I substitute the result in expr_3, it returns a value the same as C. But if I substitute the result in expr_1 and expr_2 respectively and then do a division, the outcome is dramatically different from C, which makes no sense at all. Is it...

## solve nonlinear equation with erf functi...

Maple 13

Following the last question: After eliminating the units, the equation is still not solved. Such kind of equation is not solvable at all, even numerically? Thanks.

PS: Is it possible to edit a posted question? Sometime I want to add more information but could not edit the old one.

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